Conventionally, there is provided an exhaust apparatus of an outboard motor equipped with a multi-cylinder four-stroke engine, and such exhaust apparatus includes: a first exhaust passage adapted to collect exhaust gas discharged through exhaust ports of cylinders in lower portion of a cylinder block of the engine and exhaust gas discharged through exhaust ports of cylinders in upper portion; and a second exhaust passage adapted to lead exhaust gas in the first exhaust passage with an upper opening being communicated with the first exhaust passage and a lower opening being communicated with an exhaust passage of an engine holder, in which the first exhaust passage and the second exhaust passage are provided separately by being arranged side by side, and a catalyst is placed in the second exhaust passage (Patent Documents 1 and 2).
Furthermore, there is also provided another conventional exhaust apparatus of an outboard motor equipped with a multi-cylinder four-stroke engine, and the exhaust apparatus includes: an exhaust collection unit adapted to collect exhaust gas from exhaust ports, and a spacer plate and a cover containing a catalyst, in which the exhaust collection unit and the spacer plate with the cover are arranged side by side in a width direction of an engine (Patent Document 3).